In many situations it is necessary for a circuit to poll a switch to determine the status or setting of that switch. For a simple on/off type switch a single serial communications line can be used. When the switch becomes more complex, however, the polling circuit may need to determine the status of a number of signals coming from the switch.
In one prior art system, multiple thumbwheel switch settings are interpreted by a control system that utilizes the setting of those switches to perform a calculation. Each thumbwheel switch produces a four bit output to indicate a switch setting from zero to nine. If multiple digits and therefore multiple switches are required a multiple of these four bits must be transmitted to the control system. If these signals are transmitted in parallel a large number of circuit interconnections are needed. This increases wiring complexity and also requires increased data transmission capability.